Various mobile equipment exists for dispensing a wide range of fertilizers onto lawns, gardens and fields. Of particular interest with respect to the present application is fertilizer spreading apparatus of the type commonly referred to as a manure spreader, which as its name implies, is typically used to spread animal wastes, such as barnyard manure. In a typical farm operation, manure is hauled from a confined holding area and dispensed as fertilizer onto fields where crops are to be grown. To this end, a variety of manure spreaders have been developed over the years to haul and distribute different types of manure. For instance, conventional box spreaders are preferred for handling dry, clumpy types of manure.
Box spreaders, well known in the agricultural implement art, include a box-like holding container in which a moveable conveyor is mounted in the bottom for transferring the material to the rear of the box. Rotating beaters, typically paddle shaped, are mounted in a transverse fashion at the rear of the box to engage and break up the material that has been conveyed rearwardly. The paddles also serve to distribute the broken up material in a swath as the spreader is transported across the field.
Even though box spreaders have proven to be effective for handling dry, clumpy manure, they have not been as effective for distributing manure that has a significant liquid content. One problem is that box spreaders are not sealed, resulting in leakage of the liquid content of the manure as it is being transported to the field, which in many instances is over publicly traveled roadways. To overcome this and other problems encountered with respect to the handling of liquid and semi-liquid manure, spreaders have been developed having V-shaped tanks with inwardly angled sides for conveying the material to auger assemblies mounted in the tank bottom, which in turn convey the material to distribution means. This type of spreader, as opposed to a box spreader, is commonly referred to as a tank spreader and is well adapted for handling cattle manure in liquid or slurry form as well as various types of dry manure, such as swine and poultry manure. U.S. Pat. No. 5,221,049, issued Jun. 22, 1993 in the name of Gilbert W. Linde et al, shows a tank spreader. In this spreader a distribution assembly expels material out of the side of the tank.
Tank type spreaders have been found to be particularly adaptable in precision farming operations where it is highly desirable to uniformly discharge and distribute manure to achieve specified coverage. Although it has always been desirable for nutrients provided by manure to be applied to areas in a field where it has been determined that such nutrients or other attributes are needed, it has only been recently that advances in technology have made it possible to expeditiously and accurately identify these areas in such field. For example, it is now possible to pinpoint critical field locations using precise data acquired via a satellite based Geographic Information System (GIS). Having identified such locations, problems are still encountered in manually controlling the discharge of material from tank spreaders to consistently achieve reliable results. Distribution systems based on operator judgement in many instances lack the accuracy needed to properly fulfill the demanding goals of precision farming.
In one common system using a tank spreader of the type shown in U.S. Pat. No. 5,501,404, issued Mar. 26, 1995 in the name of Donald A. Meyer et al, the manure or other nutrient material to be spread is initially loaded into a mobile tank and transported to the field having known nutrient deficiencies. The spreader travels over the field while its auger delivers the material to a generally horizontal slinger for distribution of the material onto the field. The width of distribution is set by the speed imparted to the material by the slingers, whereupon material coverage is determined primarily by the rotational speed of the auger along with the ground speed of the spreader. To a lesser degree the type, consistency and density of the material being distributed also affect the coverage and distribution pattern. Thus, the operator must first ascertain characteristics of the material and then coordinate ground and auger speeds selectively during operation, based on experience and knowledge of the equipment. It is acknowledged that human error along with other inherent limitations give rise to problems in a system of this nature.
U.S. Pat. No. 4,277,022 discloses a spreader for spreading sand, salt, manure or other particulate material, the spreader having a closed loop controller. In this device a continuous measurement of the actual mass flow rate is compared to a desired mass flow rate. The vehicle speed is measured and used to modify the desired rate of mass flow.